a mate brewed an IPA once an accidentlly underbitted it....think it was 25IBU when it should of been 45IBU - 3-4 drops of liquid hop extract bumped the whole batch up to what he wanted.
I agree with Fents :thumb:
Good for making late additions if you stuff up
Real hops are necessary though as they help with the formation of the break and one of the constituents of untreated hops(can't remember which or what :wha: ) is necessary for good yeast performance :thumb: